Electrically conductive composite materials have applications such as electrostatic dissipation and electromagnetic shielding. They are manufactured by dispersing conductive fillers such as metal particles, carbon black, graphite or carbon fibers in a polymer matrix. With increasing environmental awareness around the world, materials that pose less threat to the environment are now receiving more and more attention from researchers and the industry.
As a renewable natural resource with good mechanical properties, cellulose fiber enjoys advantages over other polymeric materials in environmental friendliness. “Fiber engineering”, described by Baum, is advocated as the “key to change” in pulp and paper industry1. Among the four recommended research areas, chemical modification of fibers and fiber surfaces1 holds great potential for the development of fiber-based functional paper/hybrid materials. Various paths can be adopted to modify pulp fibers, such as self-assembly multilayer scheme2, surface graft polymerization and surface coupling with smaller molecules, by introducing diverse functionalities with modest chemical usage. The engineered fibers can be potentially added into the conventional papermaking stock as “super-fiber fillers” to reduce overall cost. In the invention disclosed herein, intrinsically conducting polymer was introduced via an in-situ chemical polymerization route to impart electrical conductivity to the normally non-conductive (insulating) paper materials.
Electrically conducting polymers which include conjugated backbones and doping-induced charge carriers, are designated as the “fourth generation of polymeric materials”3 and deemed as a milestone in the progress of science. With a diverse range of properties (e.g. electrochromic property) besides the high electrical conductivity, ICPs (intrinsically conducting polymers) can potentially be used for applications such as electrochromic displays, electroluminescent devices, chemical and electrochemical sensors, biosensors and membranes. However, conducting polymers tend to be insoluble and infusible, and the resulting poor post-synthesis processibility3 has largely hindered their widespread commercial usage and exploitation. To solve this processing problem, various materials have been used as a carrier substrate by blending or through in-situ synthesis (chemically or electrochemically) of conducting polymers. Conductive textiles prepared by in-situ chemical polymerization of pyrrole are already commercially available4.
By combining intrinsically conducting polymers (ICP) with a common processable substrate such as pulp fibers, the resulting hybrid materials will inherit the mechanical and other useful properties from the carrier substrates (e.g. the versatile formability) while maintaining the unique properties of the ICPs. Notably, the intractability of ICPs can be easily resolved by processing the engineered fibers into desired articles. Moreover, it is well known that cellulose fiber is a renewable natural resource with superior advantages over other polymeric materials in its environmental friendliness. The small amount of polymer introduced will not have much impact on the overall biodegradability of the material. Therefore, the engineered fibers can be manufactured into disposable or recyclable products for various applications. Even for lower-end applications such as electrostatic dissipation (ESD) packaging, with the contemplated increasing demand of paper packaging materials in the future, the potential market is quite attractive both from environmental and economic considerations. There are a number of studies on ICP-paper (wood fiber) hybrid materials5;6; however, they were fairly preliminary with no or little optimization or characterization.
U.S. Pat. No. 4,617,228 to Newman et al. discloses methods for the production of electrically conductive composites such as fiberglass fabrics, with a pyrrole polymer in the pores of the porous material using a method involving treating the porous substance with liquid pyrrole, and then using a strong oxidant in the presence of a non-nucleophilic anion so that the pyrrole monomer is oxidized to a pyrrole polymer that precipitates in the interstices of the porous material.
U.S. Pat. No. 4,496,835 to Maus et al. discloses an electrically conductive composite or structural material using a dielectric substrate such as fiberglass fabric, and a layer of a pyrrole polymer on the substrate. This is then treated with a solution of a strong oxidant containing a non-nucleophilic anion, after which the substrate is dried and then exposed with vapors of a pyrrole such that the pyrrole is oxidized by the strong oxidant which forms a polypyrrole layer or film on the substrate.
U.S. Pat. No. 4,877,646 issued to Kuhn et al. discloses methods for making electrically conductive textile materials. More particularly, fabrics are rendered electrically conductive by contacting the fabric with an aqueous solution of a pyrrole compound, an oxidizing agent and a doping agent or counter ion and then depositing onto the surface of individual fibers of the fabric a prepolymer of the pyrrole compound. The prepolymer is adsorbed into the surface of the textile to give a film electrically conductive polymerized compound on the textile.
U.S. Pat. No. 4,521,450 issued to Bjorklund et al. discloses methods of increasing the electrical conductivity of impregnable materials, such as cellulose-based insulating materials, by infiltrating and polymerizing a pyrrole compound such as pyrrole and N-methylpyrrole, to give a polymer with higher electrical conductivity than the impregnable material on the material.
U.S. Pat. No. 4,604,427 issued to Roberts et al. discloses methods for forming an electrically conductive polymer blend in which a non-porous, swellable or soluble host polymer is impregnated with a compound selected such as pyrrole, aniline and a chemical oxidant which is dissolved in a solvent capable of swelling or solubilizing the host polymer. Upon polymerization the porous material so impregnated has a conductive layer.
U.S. Pat. No. 6,019,872 issued to Kurrle discloses a paper product prepared from a bleached chemical papermaking furnish containing lignin containing fibers. Incorporating low concentrations of high lignin content fibers into a chemical paper produces a paper product which can be authenticated with a phloroglucinol stain.
U.S. Pat. No. 5,779,857 issued to Norlander discloses a method for producing defibrated cellulose product having a fibrous structure with good compressibility under the influence of heat and pressure. The structure is obtained by cross-linking, in a dry state, cellulose fibers which are impregnated with a cross-linking agent and a polyfunctional alcohol.
U.S. Pat. No. 5,833,884 issued to Child discloses a method of depositing a conductive polymer film on textile fabrics using oxidative polymerization of a pyrrole compound in the presence of a dopant anion and a stabilizing agent having the formula.
U.S. Pat. No. 5,968,417 issued to Viswanathan discloses conducting compositions, and fibers or fabrics with improved anti-static properties produced by contacting the fiber or fabric with a conductive composition of formaldehyde-based resins and curing the fiber or fabric. The conductive compositions include linearly conjugated pi.-systems and sulfonated polyaryl compounds in which aryl rings of the sulfonated polyaryl compound are substituted with hydroxy, methoxy, ethoxy, hydroxymethyl, or 2-hydroxyethoxy substituents.
U.S. Pat. No. 6,228,217 issued to Dickerson et al. discloses a process for making an aqueous papermaking suspension containing a polyelectrolyte complex. The process includes using an aqueous suspension of pulp fibers containing a water-soluble cationic polymer and a water-soluble anionic polymer which react in the aqueous suspension to form a polyelectrolyte complex and a multivalent cation having a +3 charge and forming the polyelectrolyte complex. The aqueous suspension of pulp fibers contains surface active carboxyl compounds and water-soluble anionic compounds. The aqueous papermaking suspension is then sheeted and dried to give paper exhibiting enhanced strength.
U.S. Pat. No. 6,083,562 issued to Rodriguez et al. discloses methods and compositions for making antistatic fibers. The process includes forming a polymeric fiber with the fiber including a conductive component having at least 15 wt % electrically conductive particles. The polymeric fiber thus formed is mixed with monomers of a conductive polymer for a time sufficient to suffuse the monomers into the fiber after which the monomers are polymerized to form a fiber with an interpenetrating conductive polymer phase which is the conductive polymer. The conductive fiber-forming polymer may be polypyrrole and polyaniline, in which the polymer is formed in situ and is interspersed among the carbon particles of the second component.
U.S. Pat. No. 5,211,810 issued to Bartholomew et al. discloses electrically conductive polymeric materials produced by suspending a fibrous based material and a monomer precursor of a conductive polymer in an aqueous solution to which a chemical oxidant is added thereby inducing polymerization of the monomer which results in the fibrous based material being coated. The products of the process are useful as microwave food packaging.
Therefore it would be very advantageous to provide electrically conductive paper composites prepared from pulp modified with a conducting polymer and unmodified pulp which can be formed into useable products such as conducting paper.